The present invention relates to a universal joint suspension element and more particularly to a universal mechanical linkage for connection between a first movable body, such as a seat portion of a chair, and a second movable body, such as a support column or base portion of a chair.
Universal joints are well known in the art. In general, a universal joint is a shaft coupling which is capable of transmitting rotational movement from one shaft to another not colinear with it. The joint typically comprises a planar member having four rigid arms extending from a central point (commonly called a spider), wherein the arms form a pattern of two lineal bars which are substantially perpendicular to one another. The ends of the two rigid arms that form one of said lineal bars are connected by bearings to a U-shaped element which is adapted to be connected to one of the rotational shafts. The other two ends of the other two rigid arms that form the second lineal bar are also connected by bearings to a second U-shaped element which is driven by a second rotational shaft. Thus, the rotational coupling from one shaft to another not colinear with it is achieved.
U.S. Pat. No. 3,512,419 discloses another form of universal joint suspension element for use in free-rotor displacement type gyros. That patent teaches the use of torsion arms that can flex and twist instead of rigid arms. However, that patent discloses a universal joint having only two degrees of freedom. Moreover, as disclosed in that patent as a desired characteristic, the element has the characteristic of high angular compliance and extreme rigidity.
The use of a mechanical linkage in a system whereby two mutually movable members are present, such as a seat portion and a base portion of a chair, is disclosed in U.S. Pat. No. 4,185,803. That patent, however, teaches the use of concentric rings and torsion bars. The use of such rings unduly complicates the system and adds to the cost thereof.